Why it when change contacts on my phone it changes them on my mom and dad's as well

My family and I recently got iPhones for Christmas. One for my dad, one for my mom, and one for me.  We also have an iPad 2.  They are all hooked up to iCloud via one username.  When we got the phones, we had trouble transferring our contacts from our old verizon phones to our new apple ones but we eventually got the contacts we needed.  At first, my mom's phone was not connected to the iCloud account shared by the rest of us and the iPad.  She wanted the calendar from the iPad so I deleted the account on her phone and added the iCloud account that the iPad was using.  All was fine until my dad and I realized that our contacts were wiped from our phones and replaced with my mom's.  I then started painstakingly deleted my moms contacts and replacing them on my own on my phone.  However, contacts were being deleted from my mom and dad's phone at the same time.  It's almost like the three phones are constantly synching with each other.  It would be ideal if we could get all of our contacts back the way they were before my mom changed her account but we would settle for this constant synching to stop. Please give us some direction here, we are new to this. Thanks in advance!